living-cells-interview-question

// 1. Any live cell with fewer than two live neighbors dies, as if caused by under-population.
// 2. Any live cell with two or three live neighbors lives on to the next generation.
// 3. Any live cell with more than three live neighbors dies, as if by over-population..
// 4. Any dead cell with exactly three live neighbors becomes a live cell, as if by reproduction.


const input = [
  [0, 0, 1],
  [0, 0, 0],
  [0, 1, 1]
]

function applyCellRules(cellGroups){
    return cellGroups.map((cellGroup, cellGroupIdx) => {
      return cellGroup.map((cell, cellIdx) => {
        // Gather cell neighbors //
        let neighborCellCount = 0

        // Get current row neighbors
        neighborCellCount += countNeighborCells(cellGroup, cellIdx)

        if (cellGroupIdx !== 0) {
          // Get cells below
          neighborCellCount += countNeighborCells(
            cellGroups[cellGroupIdx - 1],
            cellIdx
          )
        }

        if (cellGroupIdx < cellGroups.length - 1) {
          // Get cells above
          neighborCellCount += countNeighborCells(
            cellGroups[cellGroupIdx + 1],
            cellIdx
          )
        }

        return processCellRules(cell, neighborCellCount)
      })
    })
}

function countNeighborCells(cellGroup, cellIdx) {
  // Get current cell position
  let neighborCellCount = cellGroup[cellIdx]

  if (cellIdx !== 0) {
    // Get cell to left
    neighborCellCount += cellGroup[cellIdx - 1]
  }

  if(cellIdx < cellGroup.length - 1){
    // Get cell to right
    neighborCellCount += cellGroup[cellIdx + 1]
  }

  return neighborCellCount;
}

function processCellRules(originalCell, neighborCellCount) {
  if (originalCell === 0) {
    return applyDeadCellRules(neighborCellCount)
  }

  return applyLiveCellRules(neighborCellCount)
}

function applyLiveCellRules(neighborCellCount) {
  if (neighborCellCount < 2) {
    return 0
  }

  if (2 <= neighborCellCount <= 3) {
    return 1
  }

  if (neighborCellCount > 3) {
    return 0
  }

  throw new Error(`No rules match neighborCellCount: ${neighborCellCount}`)
}

function applyDeadCellRules(neighborCount) {
  if(neighborCount === 3){
    return 1;
  }
  return 0;
}

applyCellRules(input)